The overall aim of the proposed studies is to evaluate the relationship between odor stimulation and the functioning of olfactory bulb circuits. Intracellular recordings, which will enable both membrane potential changes and patterns of activity to be examined, will be obtained from olfactory bulb neurons during the controlled, monitored delivery of odor pulses and ramps. The in vivo tiger salamander preparation, which is particularly suited for olfactory research and comparable to higher vertebrates, will be studied. In the preliminary intracellular studies, depolarizing and hyperpolarizing potentials recorded in response both to odor pulses and to electrical stimulation have been found to resemble the synaptic potentials elicited by electrical stimulation in the turtle and the rabbit, as described by others. However, the preliminary studies have also shown that odor pulses can elicit sequences of these potentials and spikes not seen in response to electrical stimulation. The goal of the present proposal is to define, for the first time, the intracellular response sequences in different types of single neurons, using a variety of odorants and concentrations as stimuli. The recorded cells will be labeled for morphological study by intracellular injection of horseradish peroxidase. In separate studies, extracellular injections of HRP will be made into sublaminae of the bulb. These extracellular injections should provide additional information about the distribution and branching patterns of groups of cells relative to each other, and serve as an additional basis for evaluating the results of the intracellular studies. The correlated analysis of the functional and structural properties of the bulbar neurons is anticipated to provide new and significant information about the processing of odor information in olfactory bulb circuits.